Masonry, a term used generically to describe building materials such as concrete, asphalt, brick, tile, stone, grout, and like substances, is used extensively in the construction of buildings, roads, parking ramps, driveways, garage flooring, fireplaces, fireplace hearths, and counter tops. When left unprotected, masonry surfaces quickly discolor from exposure to water- and oil-based stains and gradually deteriorate from spalling and efflorescence induced by water penetration and weather exposure. Common household liquids are among the most severely discoloring stains including motor oil, brake-oil, transmission fluid, cooking oil, coffee, and wine.
Masonry and other porous surfaces may be made resistant to water and water-based liquids in one of two ways: by rendering the surface waterproof or by rendering the surface water repellent. A waterproofed surface is completely impervious to both liquid water and water vapor. A water repellent surface repels water but is substantially permeable to water vapor. Mason Hayek, "Waterproofing and Water/Oil Repellency," 24 Kirk-Othmer Encyclopedia Of Chemical Technology 460-62 (3d ed. 1979), for example, provides an overview of these effects.
Waterproofing of a surface is typically achieved by application of a membrane such as vinyl chloride, polyvinyl chloride, polyethylene, or butyl rubber or by application of a sealant such as tar, asphalt, paints, polyurethane, epoxy or mastics. While these waterproofing agents can offer excellent resistance to penetration by water and water-based liquids, they often disadvantageously alter the appearance of the coated surface, changing the color of the surface and leaving it with a shine. Waterproofing treatments also trap moisture within the treated surface, thereby promoting spalling.
In contrast, water repellents do not alter the appearance of a porous masonry surface when applied as a treatment, and because a water repellent surface is permeable to water vapor, moisture does not become trapped in the masonry and spalling effects can be reduced. Water-repellent treatments used commercially include metal stearates, oils, waxes, acrylates (both polymers and monomers), silicones (solvent-based and emulsion), siliconates, silanes and, more recently, fluorochemicals. These compositions generally contain hydrophobic groups, such as a long-chain alkyl group or polydimethylsiloxane, and functional groups, such as silyl or carboxyl, to bond either covalently or ionically to the masonry surface, which typically contains high concentrations of silicon, calcium and aluminum atoms. Treatments made from these compositions are typically delivered from volatile organic solvents, which are undesirable because of the adverse environmental and health effects associated with them.
Environmental concerns have spawned the development of a number of water-dispersed and water-emulsified masonry treatments. U.S. Pat. No. 4,648,904 (DePasquale et al.), for example, describes a shelf-stable aqueous emulsion useful to render a porous ceramic substrate water-repellent consisting essentially of a C.sub.1 -C.sub.20 hydrocarbyl or halogenated hydrocarbyl silane and a nonionic emulsifying agent having a hydrophillic-lipophilic balance (HLB) value from 4 to 15. Also, U.S. Pat. No. 4,517,375 (Schmidt) discloses aqueous impregnation solutions prepared from hydrolyzed alkyl trialkoxy silanes. While providing ecological advantages over solvent-based treatments, these water-dispersed and water-emulsified silane materials have not been evidenced to provide performance comparable to solvent delivered materials. Additionally, silane compositions do not provide significant protection from oil-based stains.
Only fluorochemical-containing treatments offer significant repellency to oil-based stains. U.S. Pat. No. 5,274,159 (Pellerite et al.), for example, describes certain water-soluble or dispersible fluorocarbylalkoxysilane surfactants which may be cured onto a masonry surface. Additionally, Published World Patent Application WO 9207886 describes an aqueous dispersion of a gelled particulate fluororesin that can form a protective film having good weatherability and good stain-resistance.